This invention relates to a method for making improved split journal bearings wherein relieved areas on bearing surfaces are provided by masking such areas during overplate operations.
Journal bearings, such as those used with journal crankshafts in automobile engines and the like, are generally formed in two parts, known as bearing half shells, which are fitted into cylinder block and/or connecting rod housing bores to provide a superior bearing surface. This type of bearing is known as a split journal bearing and is a high precision, critical part that is manufactured to exacting tolerances.
In the manufacture of split journal bearings, it is important that the height dimension of the bearings be maintained within very close tolerances, measured in ten thousandths of an inch. To keep the two halves of the bearing properly located within the journal bore of the connecting rod, the two halves are forced against one another and crushed slightly to assure a continuous bearing surface and proper fit. Crush relief is provided on the bearing surface of split journal bearings to accommodate any slight deformation caused by the forcing of the two halves into engagement. Crush relief is normally about five to fifteen ten thousandths of an inch in depth. That is, wall size is reduced that amount in the crush relief areas with respect to adjacent areas.
Referring to FIG. 1, the prior art method of providing crush relief is to use material removal techniques for reducing the wall thickness of the bearing lining adjacent the parting face of the bearing prior to the final plating operation. The material removal technique may be broaching wherein a special broach arbor having a series of broaching elements for broaching the wall thickness of the bearing is provided that includes one or more broach elements for broaching the crush relief region. Alternatively, if the bearing wall thickness is formed by high speed boring operation the wall thickness of the bearing is formed by a first boring tool while the crush relief is formed by a second boring tool with an increased bore diameter and offset boring tool axis. With either technique forming crush relief in the bearing lining material adds cost to the manufacturing process and tooling.
After the crush relief area is formed on a bearing lining, the entire inner surface of the bearing is overplated by normal electroplating techniques. One problem with overplating split journal bearings is that overplate may build up at the parting face of the bearing. Build up of overplate at the parting face can cause the bearings to exceed the strict bearing height specifications and result in finished bearings being rejected as scrap.
During plating operations, the bearings are tenuously held by a plating rack since it is heretofore been considered improper to make any contact with the inner bearing surface during the overplating operation that would interfere with even application of plating material on the entire inner surface of the bearing.
In the manufacture of score chamfer type bearings, a high production type of bearing, the score chamfer bearings are retained on a magnetic wand type of rack. With this type of rack adjacent bearings may overlap one another on occasion causing irregularities in the overplate that are rejected upon inspection. The preferred type of plating rack is an end pressure contact rack wherein the ends of a contiguous line of bearings are held under pressure. However with score chamfer type bearings, minor imperfections in the score chamfers may result in the rack of bearings dislodging during the plating operation. The central problem with either type of plating rack is the difficulty in positively holding the bearings during plating.
Thrust bearings, or flanged bearings, include radially extending flanges on axially spaced ends of a journal bearing portion. Flanged bearings are frequently tightly fit within a journal opening and require relief at the flange faces because when the two halves of the flanged bearing are pressed together some limited amount of relief is required to prevent interference that may be caused by the crushing of the two bearing halves together. Therefore, it is necessary to provide flange relief on the flanges immediately adjacent the parting face of the two flanged bearing halves.
Flange relief is normally formed by a broaching operation subsequent to the wall and crush relief broaching operations. The flange face relief operation requires fixturing and broaching as a separate operation on both sides prior to shear broaching the fixtured bearings to proper length.
Flanged grooves are sometimes provided in flanged bearings to facilitate the flow of oil from the cylindrical bearing surface to the flanged bearing surfaces. The prior art manufacturing techniques for producing flange grooves is to mill, coin or broach the flange grooves into the flanges. Any of these operations require a separate fixturing set up and manufacturing step from the wall broaching and flange relief broaching operations.